First of all, absolutely NO-ONE on here is going to judge you or call you names. There but for the grace of god go many of us. Sometimes it's down to nothing more than luck who ends up accidentally pregnant and who doesn't. There aren't many young women who can honestly say they never took a stupid risk with their birth control, or never had a situation where sex took them by surprise and they were unprepared. Especially at your age.
It's great that you are only around four weeks or so, because you have plenty of time to really think this through and look into your options. But don't waste loads of time by sticking your head in the sand because those options get fewer and harder the more time goes by.
I'd really suggest confiding in a teacher, or perhaps a good friend's mum, if you can think of one who seems friendly and approachable? Please don't worry about being judged. I bet they will really surprise you about how kind and understanding they can be, but hey, if they do seem a bit judgemental it's still part of the school's job to make sure you get the support you need. And you say they judge you already, right? So what do you have to lose? Nothing!
Even if it's a teacher you don't know well personally, if there one who is young and female and has a reputation for being kind and approachable, then pick her. I can pretty much guarantee you in a school full of female teachers there will be at least one or two who have needed to get a termination, or found themselves with an unplanned baby. I promise. Teachers are fallible human beings too.
If you can't think of anyone there will be someone at school who is in charge of pastoral care, so find out who that is and go to them. This is the kind of thing they are there for.
You can also google your local British Pregnancy Advisory Service for their nearest drop in centre where you can speak to a professional who will meet young people like you every day and be able to talk you through everything you need to know.